Pedicle skin flaps, 3.5 x 9 cm, were elevated on the backs of guinea pigs. The average extent of necrosis in our flaps was 30 percent ranging 20 to 45 percent. Flap survival was improved if flap elevation has preceded by a "delay" procedure. Metabolic activities of undelayed flaps were compared with those of delayed flaps by measuring tissue metabolite levels and enzyme activities of carbohydrate metabolism. The distal end of the undelayed flaps destined to undergo necrosis exhibited a low glucose (less than 50 percent of normal) but high lactate levels (2 to 3 times normal) immediately following flap elevation. In vitro study revealed that the dying protion of the flaps had a reduction in the production of CO2 and lactate from 14C-labeled glucose. The mid-region of the flaps destined to survive displayed no significant alteration in the tissue metabolite levels, but exhibited increased CO2 production, lactate formation, and synthetic activities from glucose-C014 as well as increased glycolytic enzyme activities. Delay procedure (consisted or parallel incisions with undermining, preserving cephalic and caudal pedicles) resulted in a distribution gradient of glucose and lactate within the flaps during the initial 3 days. The caudal portion of the flap appeared to have a marginal nutrient supply but exhibited increased glucolytic enzyme activities. These increases in enzyme activities may represent an example of tissue adaptation to the altered tissue environment for tissue survival per unit blood supply. The flaps exhibited no distribution gradients of glucose and lactate within the flaps during 7 to 14 days postoperatively when the flap could be raised safely. The flaps raised after 7 days of delay displayed even distribution of metabolites and exhibited marked increases in glycolytic enzyme activities throughout the flaps. Further study will include assays of overall metabolic rates of 14C-labeled glucose of undelayed and delayed pedicle flaps and free flaps. The response of each tissue component of skin flaps will be characterized by quantitative histochemical studies.